Currently, moving objects exist in every empty space such as on ground, on and in water, in air, or in space, and thus, how to prevent accidents between the moving objects has become an important matter. In this respect, in air traffic control, the safety of air traffic is ensured by managing current and future flight states of a plurality of aircrafts to be controlled such as geographical position, altitude, direction of travelling, and ground speed and by appropriately controlling the plurality of aircrafts. In air traffic control, other than the information described above, various information items such as flight plans and weather information are collected and used. For this reason, in air traffic control, it is extremely desirable that the flight status of the plurality of aircrafts be presented in a manner where an air-traffic controller can visibly and easily recognize the status.
In the Patent Document 1 described below, a method is proposed, in which the terrain and flying positions (geographical position and altitude) of aircrafts are three-dimensionally displayed, and in a case where the distance between two adjacent aircrafts is shorter than a safe interval, a mark requesting monitoring is three-dimensionally displayed. Furthermore, in FIG. 9 and paragraph 0062 in the Patent Document 1 described below, a method is proposed, in which the predicted arrival positions of two aircrafts, which have come into the distance requiring monitoring, at the time after each scanning period from the current position is predicted, and in a case where any one of the predicted arrival positions of both the aircrafts overlaps a predetermined distance range, it is determined that there is a possibility of a conflict and the mark requesting monitoring is displayed.